The present invention concerns equipment for the leaching of solid matter from a sludge with the aid of a gas containing oxygen, the said equipment comprising a tall reactor equipped with a central pipe and an upward-directed double-action mixer at the bottom of the reactor. The mixer is situated in the vicinity of the lower edge of the central pipe: the upper blades of the mixer produce a downward suction flow from the central pipe and the lower blades disperse the gas to be fed into the sludge in the form of small bubbles, thereby preventing the solid matter from settling to the bottom of the reactor.
In leaching of a sludge containing solid matter, such as for example metal concentrate, it is important that the participatory oxygen in the leaching, being introduced in the form of oxygen or gas containing oxygen, must firstly dissolve into the solid-containing sludge, in order that the oxygen can participate in the leaching reactions of the solid matter. A tall reactor is used for the improvement of the dissolution of the oxygen, whereupon, as compared to normal atmospheric reactors, great hydrostatic pressure forms at the bottom of the reactor (1.5-3.0 atm, i.e. 0.15-0.30 MPa), due to which the oxygen dissolves well in the reaction solution and thereby catalyses the dissolution of the solid matter.
In the prior art it is known for example U.S. Pat. No. 4,648,973, wherein the equipment concerns a reactor with a height many times greater than its diameter, inside which is located a concentric pipe. The sludge is fed into the upper part of the central pipe, as is the oxygen. For recirculation of the sludge, the central pipe is equipped with a mixer suspended from the top downwards, which pumps the sludge down the central pipe and the sludge then passes up through the space between the reactor and the internal pipe.
The ratio between the diameters of the central pipe and outer pipe is between 0.4 and 0.85.
Now, the present invention being developed concerns an equipment that comprises a tall reactor for the leaching of solid matter from a sludge, such as metal concentrate. The height of the reactor is many times greater than its diameter and the reactor is equipped with a central pipe extending to the bottom part, a mixer being located in the vicinity of the lower part of the central pipe and a feeding member for gas containing oxygen. The shaft of the mixer extends upwards from the bottom of the reactor. The mixer itself consists of an essentially horizontal central plate, with curved blades fixed above It and essentially straight blades fixed underneath the plate. The blades located above the central plate produce a downward sucking flow of sludge from the central pipe and, with the aid of the blades below the plate, the gas containing oxygen to be fed into the lower at of the reactor is dispersed into the sludge in the form of small bubbles, thereby preventing the sludge from precipitating to the bottom of the reactor. The essential features of the present invention are laid out in the enclosed claims.
As mentioned above, it is essential to the equipment that the mixer is located in the immediate vicinity of the lower edge of the central pipe, whereby the cross-section area of the discharge orifice remaining between the central pipe and the mixer is less than half the cross-section area of the central pipe, preferably at most one third of the cross-section area of the pipe. Thus the flow rate, from the central pipe, of the downward-flowing sludge increases at least twofold in comparison to the flow rate taking place in the central pipe. The nearer the mixer is located to the lower end of the pipe, the better the suction building up to the central pipe. In practice the limit is set by the tolerances, which result from the bending of the shaft and from the flexibility and dimensioning of the other parts. At the aforementioned cross-sectional area ratio, such a flow rate is achieved that the downward-directed solution flow is faster than the climbing rate of the gas bubbles, and the upward flow rate of the solution in the casing of the reactor is greater than the settling rate of the particles of solid matter.
The mixer used in the method according to the invention is of double-action, it is formed of two parts having an essentially horizontal plate between them. Curved blades are fixed above the horizontal plate which suck sludge downward in the central pipe. The blades fixed underneath the horizontal plate form a straight-bladed turbine mixer. As the gas containing oxygen is fed underneath the mixer installed in the bottom part of the reactor, the lower part of the mixer disperses the feed gas into very small bubbles, thus assisting the dissolution of the gas into the sludge. As the gas is fed into the sludge at the bottom part of the reactor, the gas bubbles moving with the sludge flow have as long a residence and reaction time in the sludge as possible, before they reach the surface or descend with the flow to be recirculated through the central pipe.